Topically applied pharmaceutical compositions that exist in the liquid state and are present as a foam when applied are familiar. For example, EP 0 510 561 B1 describes one such pharmaceutical composition applied as foam, wherein the basic liquid used in the known pharmaceutical composition is foamed exclusively by mechanical action. The basic liquid composition that is mechanically foamed contains, as ingredients, a surfactant as the foaming agent, a solvent or mixture of solvents, as well as a pharmaceutical active ingredient, wherein this known liquid composition should be foamable simply by mechanical action, without the use of a propellant. In example 5 of EP 0 510 561 B1, one such known composition is described, containing an aqueous alkylamidobetaine solution as the surfactant. In addition, the composition described in this example is provided with lecithin, which serves solely to form liposomes.
In order to be able to measure the foaming behavior of liquid compositions, various measurement techniques are known and also standardized, such as by DIN Standard 53902. The particular liquid composition being investigated is subjected to a more or less reproducible mechanical action for a given time in order to create a foam, whose volume and stability are measured. According to DE 197 40 095 A, however, known measurement techniques do not adequately distinguish between the foam volumes and foam stabilities of compositions which are similar in terms of their ingredients. DE 197 40 095 A proposes foaming the liquid composition being measured by using a stirrer with a given profile, which is driven at a given speed of rotation. The foam created in this way is visually measured.
A further development of this foam measuring technique is described in EP 1 092 970 B1, wherein the development differs from the measurement technique previously described in reference to DE 197 40 095 A by providing an automatic determination of the height of the foam via measuring electrodes. This measurement method, which is called the “SITA measurement method” in the present text, allows one to determine the foam volume on the one hand, and on the other hand the foam stability of liquids, especially dyeing and cleaning solutions, electroplating agents, emulsions, rinsing agents, body care products or even beer, so as to obtain a quality rating of the aforementioned foamable liquids.
When one needs to develop liquids that are foamable and therefore are applied as a foam in the field of pharmacy, it is usually proposed to proceed by selecting a pharmaceutically active liquid and one then attempts to foam it by varying the mechanical foaming technique, in particular, by varying the air pressure, the geometry and configuration of the foam head and the valve of a particular foam applicator. However, such a development process for foamable, originally liquid, pharmaceutical compositions is very time intensive and may suffer from a drawback such that a foam differing in composition and essentially inhomogeneous can result from varying the configuration of the aforementioned parameters of the mechanical foam applicator.
Thus, one underlying problem of the present invention is to provide a method for the development of a liquid pharmaceutical composition to be applied as foam to the skin, by which the development time for such pharmaceutical compositions is substantially simplified and shortened. Further, another underlying problem of the present invention is to provide a topically applicable composition that can be applied as foam and that contains a systemically or topically acting pharmaceutical active ingredient, and, may be, for example, be developed by the disclosed processes.